This invention relates to techniques of flame-retardant adhesives to be used in producing circuit materials employed in, for example, electronic instruments.
In recent years, there have been employed circuit materials such as flat cables as connectors for connecting connection terminals of different wiring boards of electronic instruments such as personal computers.
Such a circuit material consists of a definite number of conductors located between a pair of coating materials which are bonded to each other by, for example, thermo compression bonding. Since temperature is generally elevated to a considerably high level in electronic instruments, flame-retardant adhesives are required to bond coating materials.
There are known adhesives to be used in these circuit materials which contain halogen-based flame retarders or ammonium polyphosphate.
However, the conventional adhesives for circuit materials containing halogen-based flame retarders suffer from a problem that they generate halogen gases in the course of combustion and thus exert undesirable effects on the environment.
On the other hand, the conventional adhesives containing ammonium polyphosphate suffer from another problem that they are poor in the thermo-humidity resistant electrical characteristics, though they do not adversely affect the enviroment.
Although it is proposed to solve these problems by using an adhesive containing a nitrogen compound and zinc borate, this adhesive has a disadvantage of having a somewhat poor flame retardancy.
The present invention, which has been completed to solve the above described problems encountering in the prior art, aims at providing flame-retardant adhesives which are harmless to the environment, show excellent thermo-humidity resistant electrical characteristics and have high flame retardancy, and circuit materials with the use of these flame-retardant adhesives.
According to the first aspect, the present invention provides a flame-retardant adhesive which contains a saturated polyester resin and a flame retarder containing a component having Pxe2x80x94C bond in its molecule and a component having nitrogen in its molecule, wherein the content of the flame retardant amounts to 90 parts by weight or more and 120 parts by weight or less per 100 parts by weight of the saturated polyester resin.
According to another aspect, the present invention provides a flame-retardant adhesive which comprises a saturated polyester resin and a flame retarder containing a component having Pxe2x80x94C bond in its molecule, a component having nitrogen in its molecule and an acid component free from phosphorus in its molecule.
The present invention further provides the flame-retardant adhesive as described above wherein the content of said flame retarder amounts to 80 parts by weight or more and 120 parts by weight or less per 100 parts by weight of the saturated polyester resin.
The present invention further provides the flame-retardant adhesive as described above wherein the component having Pxe2x80x94C bond in its molecule contained in said flame retarder is nitrilotrismethylenephosphonic acid.
The present invention furthermore provides the flame-retardant adhesive as described above wherein the component having nitrogen in its molecule contained in said flame retarder is melamine.
The present invention furthermore provides the flame-retardant adhesive as described above wherein the acid component free from phosphorus in its molecule is a compound containing melamine and cyanuric acid.
According to another aspect, the present invention provides a circuit material for electrically connecting electrodes to each other which comprises a definite conductor for forming a circuit, and coating materials for coating the conductor, wherein the coating materials are adhered by using a flame-retardant adhesive which comprises a saturated polyester resin, and a flame retarder containing a component having Pxe2x80x94C bond in its molecule and a component having nitrogen in its molecule, and in which the content of said flame retarder amounts to 90 parts by weight or more per 100 parts by weight of said saturated polyester resin.
According to another aspect, the present invention provides a circuit material for electrically connecting electrodes to each other which comprises a definite conductor for forming a circuit, and coating materials for coating the conductor, wherein the coating materials are adhered by using a flame-retardant adhesive which comprises a saturated polyester resin, and a flame retarder containing a component having Pxe2x80x94C bond in its molecule, a component having nitrogen in its molecule and acid component free from phosphorus in its molecule.
Because of containing a halogen-free flame retarder, the flame-retardant adhesive according to the present invention generates no halogen gas in the course of combustion and, therefore, does not adversely affect the environment.
Because of containing a component having Pxe2x80x94C bond in its molecule and a component having nitrogen in its molecule, on the other hand, the flame-retardant adhesive according to the present invention exerts a synergistic effect of promoting the formation of a surface coating film, which has effects of blocking heat and oxygen, due to the condensation reaction of phosphorus in the course of combustion and forms water-insoluble salt, thereby improving the resistance against hydrolysis. As a result, the thermo-humidity resistant electrical characteristics and flame retardancy can be improved.
In the present invention, the content of nitrogen can be further elevated by adding an acid component free from phosphorus in its molecule to the flame retarder. Thus, a flame-retardant adhesive having a desired thermo-humidity resistant electrical characteristics and flame retardancy can be obtained by using the flame retarder in a smaller amount.